This invention relates in general to a means for varying the back pressure in an exhaust system for internal combustion engines and more particularly, to a power control valve attachment for assembly to a back pressuring exhaust system of a two cycle motorcycle type engine for producing a variable back pressuring of the engine under varying operating conditions thereof.
Back pressuring exhaust control valves have been employed heretofore with two cycle type engines as in the McKechnie U.S. Pat. No. 1,318,781 and Junkers U.S. Pat. No. 1,320,062. In the McKechnie patent, a spring biased flap valve was employed as close to the cylinder exhaust port as possible for throttling exhaust gases just prior to closure of the port by the cylinder. In Junkers, a biased, or otherwise controlled valve was employed for restricting gas flow from an exhaust chamber in an effort to produce a substantially constant back pressure on the engine cylinder. Neither of these valve constructions were suitable for use as an attachment to a pre-existing exhaust system of the type currently in use.
Currently, it is common practice to utilize specially designed back pressuring exhaust systems for the two cycle type engines in use on motorcycle engines. In such two cycle engines, the fuel and air charge is introduced through a port in the cylinder side wall at the same time that exhaust gases are being forced out of the cylinder through another port in the side wall of the cylinder under influence of the return stroke of the cylinder. Specially developed exhaust systems have been designed heretofore to provide just the right back pressure upon the exhaust gases during their evacuation to allow for the exhaust of exhaust gases, yet prevent the exhausting of the charging fuel and air mixture being introduced preparatory to a ignition and power stroke. However, the back pressure characteristics of the exhaust system must be carefully determined for the expected operating conditions of the vehicle, as for example, hill climbing versus street riding.
It has been common heretofore to provide a duct section in exhaust system, commonly referred to as a "stinger" with a minimum cross sectional diameter for the system to provide the desired back pressure of the system. In some exhaust systems, the stinger is replacable, while in others a removable orifice disc may be inserted into the stinger to provide a desired back pressure for an expected engine operating condition. However, once the particular "stinger" or orifice disc has been assembled to the exhaust gas system, the back pressure characteristics of the system are set for operation of the vehicle.
Another prior art approach with the aforementioned type of exhaust systems is to build in a valve in the pressure chamber which presumably provides a pressure wave reflecting surface to reflect a positive pressure wave in the exhaust system, as in U.S. Pat. NO. 3,703,937. However, this approach does not lend itself to the type of attachment or assembly for pre-existing exhaust systems as contemplated in the present invention, nor is its construction or mode of operation similar to that of the present invention.
It is the primary object of the present invention to disclose and provide a power control valve attachment or assembly which may be conveniently assembled to pre-existing exhaust systems of the type hereinbefore discussed for providing a controlled back pressuring by the system during operation of the vehicle in response to engine operating characteristics to increase the power output thereof.
It is another object of the within invention to disclose and provide a power control valve attachment, as in the foregoing object, wherein the control valve means may be easily incorporated into a duct section of the pre-existing engine exhaust system to utilize the duct section as part of the valve means in a relatively inexpensive, easily assembled and maintained manner for improving the power output characteristics of the engine employed with the system.